1.
equivalent focal length
当量焦距，等效焦距
2.
Effective Fresnel Number and Focal Shifts of Focused Cylindrical Light Beams;
聚焦柱面光束的等效菲涅耳数及焦移
3.
Having three focal lengths.
三焦距的有三个焦距的
4.
Focus-to-film distance(f.f.d)
焦点-胶片距离(焦距)
5.
In taking a picture, the shutter,the focal length and the other things must be adjusted as the case may be.
在拍照过程中，快门、焦距等等必须按实际情况加以调整。
6.
autofocus zoom lens
自动聚焦变焦距镜头
7.
variable focal length (cylindrical) lens
变焦(距)(圆柱)透镜
8.
long focus lens
长焦距（望远）镜头
9.
A Study on Multi-wave Pre-stack Migration Based on Equivalent Offset
基于等效偏移距的多波叠前偏移研究
10.
Focal length: The distance between the centre of a lens and its principal focus.
焦距:镜头中心与其主焦点的距离。
11.
A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length measured in meters.
屈光度透镜或棱镜折光率的一种量度，等于以米计算焦距之倒数
12.
If very expensive, big, and heavy, may be almost as good and almost as fast at any given focal length as cheap fixed primes.
如果很贵，很大，很重，那么它几乎可以做到和那些等焦距廉价的定焦一样快和好。
13.
Macro lens: A lens which focuses on close subjects without the aid of close-up devices such as extension tubes or close-up lenses.
微距镜头:不需收近装置，如外延管，近镜等而把很近距离的物体对焦的镜头。
14.
More accurate calculations would have the same effect as focusing a lens: the picture becomes sharper.
计算越精确就有如调节焦距般的效果：图像更清晰。
15.
The numbers you specified can't be used because the interval for the minor unit tick marks must be less than or equal to the interval for the major unit tick marks.
指定的数字无效，因为次要刻度间距需小于等于主要刻度间距。
16.
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快速变焦距手术显微镜
17.
Only a bit out of focus.
只是焦距有点不对。
18.
One must focus the camera before taking a picture.
拍照之前先要对焦距。